Carrying amount of redeemable preferred stock

No definition available.

Name:	cmcsa_CarryingAmountOfRedeemablePreferredStock
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of our redeemable subsidiary preferred shares and/or stock

+ References

No definition available.

+ Details

Name:	cmcsa_FairValueAmountOfRedeemablePreferredShares
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value of a cost method investment related to redeemable preferred shares.

+ References

No definition available.

+ Details

Name:	cmcsa_FairValueOfCostMethodInvestmentRedeemablePreferredShares
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Nonredeemable preferred stock issued by a wholly owned subsidiary of the company.

+ References

No definition available.

+ Details

Name:	cmcsa_NonredeemablePreferredStock
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of Preferred Stock Series

+ References

No definition available.

+ Details

Name:	cmcsa_NumberofPreferredStockSeries
Namespace Prefix:	cmcsa_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Preferred stock aggregate redemption value

+ References

No definition available.

+ Details

Name:	cmcsa_PreferredStockAggregateRedemptionValue
Namespace Prefix:	cmcsa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Original amount of cost-method investments at the acquisition date.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfCostMethodInvestmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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- Details

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Data Type:	na
Balance Type:
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- Details

Name:	dei_LegalEntityAxis=cmcsa_NBCUniversalMediaLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Data Type:	na
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- Details

Name:	dei_LegalEntityAxis=cmcsa_AirTouchMember
Namespace Prefix:
Data Type:	na
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- Details

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Investments (Cost Method Investments) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) preferred_stock_series	Nov. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)
BuzzFeed [Member]
Schedule of Cost-method Investments [Line Items]
Purchases of investments		$ 200		$ 200
Air Touch [Member]
Schedule of Cost-method Investments [Line Items]
Number of preferred stock series \| preferred_stock_series	2
Preferred stock aggregate redemption value	$ 1,650
NBCUniversal Media LLC [Member] \| Vox Media [Member]
Schedule of Cost-method Investments [Line Items]
Purchases of investments				200
NBCUniversal Media LLC [Member] \| BuzzFeed [Member]
Schedule of Cost-method Investments [Line Items]
Purchases of investments		$ 200		$ 200
Air Touch [Member]
Schedule of Cost-method Investments [Line Items]
Number of preferred stock series \| preferred_stock_series	3
Preferred stock aggregate redemption value	$ 1,750
Redeemable subsidiary preferred shares	1,600		$ 1,600
Nonredeemable subsidiary preferred shares	100		100
Level 2 [Member] \| Air Touch [Member]
Schedule of Cost-method Investments [Line Items]
Fair value of cost method Investment redeemable preferred shares	1,700		1,700
Level 2 [Member] \| Air Touch [Member]
Schedule of Cost-method Investments [Line Items]
Fair value of redeemable preferred shares	$ 1,700		$ 1,700